Research breakthrough into DNA behind schizophrenia/bipolar

Study finds 11 regions of human genome responsible

By Ian Birch

In a major breakthrough involving 50,000 people, researchers have identified 11 regions of the human genome thought to be responsible for schizophrenia and bipolar disorder. Six of these regions were previously unknown.

The Psychiatric Genome-Wide Association Study Consortium (PGC) reports, in the current issue of Nature Genetics, that common genetic variants contribute to a person's risk of schizophrenia and bipolar disorder. The findings, the researchers say, represent a significant advance in understanding the causes of these two illnesses.

In the schizophrenia study, a total of seven locations on the genome were implicated in the disease, five of which had not been identified before. When similar data from the bipolar disorder study, which ran concurrently, were combined with results from the schizophrenia study, three gene locations were identified that proved to be involved in both disorders, suggesting a genetic overlap between schizophrenia and bipolar disorder.

"Genetic factors play an important role in the susceptibility to develop schizophrenia," Roel Ophoff from the University of California at Los Angeles (UCLA) said, "but identifying these genetic factors has been very difficult. We know that schizophrenia is not caused by a single gene that explains everything but an interplay of many genetic and non-genetic factors."

Currently, there is no objective biological marker or "sign" that can be used for diagnosis.

"This so-called heterogeneity at the genetic and clinical level is the biggest challenge for genetic studies of neuropsychiatric disorders," Ophoff said. "One way to deal with these difficulties is to increase the size of the study so there is sufficient 'power' to detect genetic effects, even amidst this clinical and genetic diversity."

The fact that even this large study resulted in a limited number of schizophrenia and bipolar genes demonstrates once again, he said, the complex nature of the disease.

Formed in 2007, the PGC is the largest consortium ever in psychiatry. Over 250 researchers from more than 20 countries have joined forces to investigate the genetic causes of mental illness. Crucial to the success of the project was the willingness of many groups to share genetic data from tens of thousands of patients collected over many years.

The research was funded by numerous European, American and Australian funding bodies. Funds for coordination of the consortium were provided by the National Institute of Mental Health in the U.S.